Concept check 27.5
1. Explain how muscles work in pairs in moving limbs.

Muscles can only pull not push another motion is needed to bring the bone to its original position that is why muscles work in pairs. When skeletal muscles contracte there is an opossing muscle that is relaxed but can contract and pull the bone back on its opposite direction.

2. Identify the structures that make up a skeletal muscle. Include these terms: muscle fiber, fascicle, myofibrils, actin, myosin, sarcomere.

muscle fiber: single long cylindrical muscle cell that contains many nuclei.

myofibrils: bundles of smaller units.

sarcomere: unit of contraction in a muscle fiber.

Myosin: composed of proteins and have bumplike projection

Actin: have a twisted structure and are composed of protein.

3. Identify at least 3 organ systems involved in a handshake. Describe WHAT each system contributes to the handshake.

Brain: the main control center in your body, decides to initiate the handshake sends messages through the nerves. 

eyes: persive the presence of another person and sends this message to the brain. 

Muscles: Perform contractions and relaxations to preform the handshake. 

4. Explain how actin and myosin interact as a muscle cell contracts.

The myosin binds to the actin, then the myosin heads bend living the actins move towards the center of the sarcomere. ATP binds to each myosin head and becomes relased  from the actin.